J.P.
I would put a baby gate up so that she isn't banging on the door, if that is a problem. Then, I would talk to the neighbors and let them know that starting Friday night (easier on weekends) that you are going to try to break this habit, and it may involve some crying. You also have to be okay with the 6 month old being woken up a couple nights. It took us 2 nights for my son to stop screaming at night and my daughter didn't even wake up. (He wanted covers, a toy, another kiss, just us, etc.) But, luckily he stays in his bed (he knows that if he doesn't he goes back to a crib. :)